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18.4 Chemical properties of fats and oils

1. Hydrolysis– Reverse of esterification– Forms carboxylic acids (FAs) and alcohol (glycerol)– Catalyst = acid or enzyme (lipase)

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Chemical reactions of TAGs

2. Saponification (hydrolysis in base)– Forms carboxylic acid salts (soaps)– Na+ = hard soap; K+ = liquid soap

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Chemical reactions of TAGs

3. Hydrogenation– Unsaturated chains add H2 (become “hydrogenated”)

– Increase the melting point (become semi-solid)

– Side effect = production of trans fats

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Olestra

• Artificial, noncaloric fat substitute (indigestible)

• FDA warning– “This Product Contains Olestra. Olestra may cause abdominal

cramping and loose stools. Olestra inhibits the absorption of some vitamins and other nutrients. Vitamins A, D, E, and K have been added.”

Reaction map for triglycerides

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18.5 Waxes

• Esters of fatty acids• Alcohol has long chain• Insoluble in water• Not easily hydrolyzed• Natural protective

coatings on plants, fruit, skin, fur, feathers

• Commercially used as candles, cosmetics

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Membrane/structural lipids

• 18.6 Phospholipids (phosphoglycerides)• 18.7 Sphingolipids (sphingomyelins and glycolipids)

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18.8 Biological membranes

• Separate contents of cells from external fluids• Semipermeable

– Nutrients enter, waste products leave

• Lipid bilayer = structural lipids and cholesterol

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Fluid-mosaic model

• Ex: Cholesterol, hormones• 4 ring structure

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18.9 Steroids

• Contains –OH• Produced by liver• Supplied by diet• Precursor for hormones, vitamin D• Component of cell membranes

– Provide rigidity

• High levels– Gallstones– Deposits on arteries

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Cholesterol

• Chemical messengers carried through the blood

• Same 4-ring structure as cholesterol

• Examples:– Cortisol: increase glucose

concentration in the body– Cortisone: anti-inflammatory

(arthritis, asthma)– Testosterone, estradiol,

estrone, progesterone: sex hormones

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18.10 Steroid hormones

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18.11 Prostaglandins

• Hormones involved in production of pain, fever, inflammatory reactions

• Synthesized from arachidonic acid (a polyunsaturated FA)• Synthesis inhibited by NSAIDs

– e.g. acetylsalicylic acid (aspirin)

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Summary of lipids